PROJECT SUMMARY/ABSTRACT Medication is an efficacious treatment strategy for adolescents with attention-deficit/hyperactivity disorder (ADHD) (Chan et al. 2016), however use significantly declines during adolescence when the consequences of ADHD are most severe (e.g. dropping out of school, delinquency, etc.). The Unified Theory of Behavior Change (UTBC) (Fishbein et al. 2001) has been proposed as a conceptual model to explain the mechanism underlying ADHD medication adherence and to guide the development of interventions to improve the continuity of treatment (Chacko et al. 2010). The UTBC is a well-established and empirically tested model that identifies factors that influence an individual?s intention to perform a behavior as well as factors that influence whether a behavior is actually carried out. Indeed, our preliminary data support the relevance of pre- intention factors and implementation factors for medication continuity among adolescents with ADHD. Currently, no evidence-based interventions target medication continuity for adolescents with ADHD. Our research team is well positioned to create an intervention that addresses each of the main UTBC factors influencing the intention and implementation of regular medicine taking. Such an intervention would transform care for adolescents with ADHD and help prevent the alarming fall-off in effect size from medication efficacy studies to effectiveness in real world practice caused by poor adherence. The overall objective of this application is to develop and test a multi-component intervention that systematically identifies and targets aspects of the UTBC model most relevant for each adolescent with poor ADHD medication continuity. Our central hypothesis is that our tailored intervention will support ADHD medication continuity. We will objectively test our central hypothesis by accomplishing the following specific aims: 1) Design, build, and optimize the usability of web-based intervention components to support medication continuity among adolescents with ADHD using an iterative stakeholder-centered design approach involving all stakeholders (i.e., adolescents, parents, and pediatricians) in all stages of development, and 2) Conduct a 12-month stepped wedge cluster randomized controlled trial among adolescents with poor medication continuity to test whether the intervention engages the mechanism underlying medication continuity and improves outcomes. Preliminary data generated from this project will be used to support a future R01 application to test the intervention in a larger stepped wedge cluster RCT that is powered to detect differences accounting for clustering within practices and to formally assess moderators and mediators of outcomes.